This invention relates to shift controls for synchronized countershaft transmissions, and more particularly, to assisting mechanisms for such controls, and specifically to a single selector rod type shifter having an electro-mechanical controller for establishing both linear and rotary motion of the selector rod.
The basic elements of a shift mechanism as it applies to a synchronized countershaft transmission require two types of force to be imposed on the main shift rail to execute a gear change. An axial force along the axis of the shift rail is required to disengage the original gear ratio and provide engagement force on the synchronizer of the newly selected gear ratio. This linear axial force is the only force necessary for "straightline" shifts such as 1-2, 3-4 and 5-6.
When "crossover" shifts are made, such as 2-3 or 4-5, a rotational force is also required to switch over from the original synchronizer (i.e., 1-2 synchronizer) to the newly selected synchronizer (i.e., the 3-4 synchronizer). The shift actuator applies these forces to the main shift rail.
Prior art mechanisms constrain the main shift rail to move through a rectangular path when making a crossover shift, such as a 2-3 shift. This type of path is difficult to follow rapidly because it requires an axial acceleration and deceleration to move from a second gear position to the neutral position, followed by a rotational acceleration and deceleration to move from the 1-2 synchronizer to the 3-4 synchronizer, and finally an axial acceleration and deceleration to move from the neutral position to the third gear position. In addition, it is required that precise timing be maintained between the axial and rotational movements in order to follow the rectangular path. These requirements constrain the speed of an actuator that follows this path.